As a result of the higher age due to medical progress and/or increased direct loads, such as from sport or work, the various joint parts of the human body are nowadays subjected to ever-increasing stress on average. In particular, the frequently used joint parts of the walking apparatus of the human body, such as the hips and knees, are to be mentioned here. In many cases, the respective joint is damaged to such an extent that a corresponding operation becomes indispensable. As a result, the number of hip and knee surgeries has risen dramatically over the last few decades and these surgeries have become a standard procedure in medical practice where a natural joint ball is replaced by prosthesis.
After such a surgery, the patient usually receives comprehensive physiotherapeutic instruction at first, but is largely on his own after leaving the clinic. In particular, incorrect, i.e. excessively high, loads caused by the patient may cause damage to the prosthesis or the surrounding tissue. To prevent this, various systems have been developed to monitor the load on the foot of a patient.
US 2016 158 622 A1 discloses a conventional walking training system comprising a treadmill and two frames that support the patient, wherein sensors measure the weight distribution while running. This system is a convention system used in physiotherapy. For private use, however, it is too expensive (because e.g. a treadmill is used), too bulky and too impractical (especially for everyday use).
U.S. Pat. No. 4,745,930 discloses a device integrated on a relatively narrow shoe sole, comprising sensor units provided in designated chambers and comprising pairs of electrical contacts which are alternately finger-shaped and can be pressed together by pressure to create an electrical contact. Unfortunately, however, this device is normally connected to a support frame via a cable for transmitting signals to it and also includes a sensitive sensor system that is integrated into the sole of the shoe and offers no readout options. This makes practical everyday use almost impossible.
US 2005 026 160 2005 026 1609 A1 discloses a device of a simple configuration integrated in a relatively wide shoe sole, comprising a state sensor that measures the physical state of the foot and an RF transmitter that sends a signal to an external display unit according to the measurement. The afore-mentioned status sensors are installed in special installation niches. Although this device is integrated into the sole of the shoe, the considerable width of the shoe's sole makes it uncomfortable. In addition, the measurement signals are transmitted by an RF transmitter, which requires an external receiver unit (e.g. a display wristband or a Smartphone) and an uninterrupted transmission path between the RF transmitter and the receiver unit.
U.S. Pat. No. 5,033,291 discloses a flexible sensor capable of measuring foot pressure distributions upon contact of the foot, said sensor comprising a plurality of flexible electrodes divided into two non-parallel sets for measuring these pressure distributions. In particular, the sensor is preferably designed in the shape of a foot. A similar flexible sensor system is also disclosed in U.S. Pat. No. 5,408,873, wherein several force sensor units may be positioned at the essential measuring points according to this invention. However, these sensors are relatively complex and expensive in their implementation as disclosed. Furthermore, the aforementioned disclosures do not provide for a feedback system.
In addition to the above-mentioned devices and systems from the medical sector, there exist also countless other systems that are used in the sports sector, most of which are only used for the direct measurement of training parameters, such as the contact time of the feet and the step frequency. Such a system is disclosed, for example, in U.S. Pat. No. 6,876,947 B1, which comprises a unit attached to the shoe that transmits measurement signals, such as the contact time of the foot, to a display unit (e.g. a Smartphone or smart watch) using RF transmission. Also this disclosure gives rise to the aforementioned problems that may arise during RF transmission and the problem of a missing (direct) feedback.